The processing and handling of mail pieces and other documents consumes an enormous amount of human and financial resources, particularly if the processing of the mailpieces is done manually. The processing and handling of mailpieces not only takes place at the Postal Service, but also occurs at each and every business or other site where communication via the mail delivery system is utilized. That is, various pieces of mail generated by a plurality of departments and individuals within a company need to be collected, sorted, addressed, and franked as part of the outgoing mail process. Additionally, incoming mail needs to be collected and sorted efficiently to ensure that it gets to the addressee in a minimal amount of time. Since much of the documentation and information being conveyed through the mail system is critical in nature relative to the success of a business, it is imperative that the processing and handling of both the incoming and outgoing mailpieces be done efficiently and reliably so as not to negatively impact the functioning of the business.
In view of the above, various automated mail handling machines have been developed for processing mail (removing individual pieces of mail from a stack and performing subsequent actions on each individual piece of mail). However, in order for these automatic mail handling machines to be effective, they must process and handle "mixed mail." The term "mixed mail" is used herein to mean sets of intermixed mailpieces of varying size (postcards to 9" by 12" flats), thickness, and weight. In addition, the term "mixed mail" also includes stepped mail (i.e. an envelope containing therein an insert which is smaller than the envelope to create a step in the envelope), tabbed and untabbed mail products, and mailpieces made from different substrates. Thus, the range of types and sizes of mailpieces which must be processed is extremely broad and often requires trade-offs to be made in the design of mixed mail feeding devices in order to permit effective and reliable processing of a wide variety of mixed mailpieces.
In known mixed mail handling machines which separate and transport individual pieces of mail away from a stack of mixed mail, the stack of "mixed mail" is first loaded onto some type of conveying system for subsequent sorting into individual pieces. The stack of mixed mail is moved as a stack by an external force to, for example, a shingling device. The shingling device applies a force to the lead mailpiece in the stack to initiate the separation of the lead mailpiece from the rest of the stack by shingling it slightly relative to the stack. The shingled mailpieces are then transported downstream to, for example, a separating or singulating device which completes the separation of the lead mailpiece from the stack so that individual pieces of mail are transported further downstream for subsequent processing. In the mailing machine described immediately above, the various forces acting on the mailpieces in moving the stack, shingling the mailpieces, separating the mailpieces and moving the individual mailpieces downstream often act in a counterproductive manner relative to each other. For example, inter-document stack forces exist between each of the mailpieces that are in contact with each other in the stack. The inter-document stack forces are created by the stack advance mechanism, the frictional forces between the documents, and potentially electrostatic forces that may exist between the documents. The inter-document forces tend to oppose the force required to shear the lead mailpiece from the stack. Additionally, the interaction of the force used to drive the shingled stack toward the separator and the separator forces can potentially cause a thin mailpiece to be damaged as it enters the separator. Furthermore, in a conventional separator, there are retard belts and feeder belts that are used to separate the mailpiece from the shingled stack. Both the forces applied by the retard belts and the feeder belts must be sufficient to overcome the inter-document forces previously discussed. However, the friction force generated by the retard belts cannot be greater than that of the feeder belts or the mailpieces will not be effectively separated and fed downstream to another mail processing device. Moreover, if the feeding force being applied to the mailpieces for presenting them to the separator is too great, another potential problem which may occur is that a plurality of mailpieces (multifeeds) will be forced through the separator without the successful separation of the mailpieces. Another problem that can occur is that the interdocument stack forces can keep the mailpieces from deskewing or bottom edge aligning which would prevent the mailpieces from separating or could also cause an over-height problem in the mail handling machine.
Another problem that can occur in the handling of the mailpieces is that the desired gap between each mailpiece may not be achieved by the document separators. The gap is important because it is necessary for timing of down stream processing such as OCR (optical character recognition). Gap also effects throughput of the mail handling machine; if the gap is too large, the throughput of the machine decreases. A buffer between document singulating apparatus may be used to assist with providing the proper gap between mailpieces and keep the mailpieces from colliding which can damage the mailpieces. When a mail handling machine has two document singulating apparatus, the down stream document singulating apparatus will function to delay processing of a mailpiece in a multipiece feed situation such that a next mailpiece can crash into the mailpiece in the downstream stream document singulating apparatus. A stopping apparatus can be used to stop the next mailpiece, this improves the gap between the mailpieces and subsequently keeps the mailpieces from colliding.
In view of the above, it is recognized that large forces are desirable to act on the mailpieces to accelerate and separate the mailpieces in a reliable and high throughput manner. However, these same high forces can damage the mailpieces being processed (i.e. buckle lightweight mailpieces) and keep the mailpieces from being bottom edge aligned. Conversely, if the forces used to accelerate and separate the mailpieces are too small, then poor separation, lower throughput, and stalling of the mailpieces being processed will result. Put in another way, thin mailpieces are weak and require low forces to prevent them from being damaged, while thick/heavy mail is strong and requires high forces for proper separation and feeding. The effect is that when the thick/heavy mail is in the stack higher stack normal forces are created thereby increasing interdocument forces and requiring higher nip forces at the separator. Thus, the structure used to separate a stack of mixed mail must take into account the counterproductive nature of the forces acting on the mailpieces and be such that an effective force profile acts on the mailpieces throughout their processing cycle so that effective and reliable mailpiece separation and transport at very high processing speeds (such as four mailpieces per second) can be accomplished without physical damage occurring to the mailpieces. However, since the desired force profile acting on a particular mailpiece is dependent upon the size, thickness, configuration, weight, and substrate of the individual mailpiece being processed, the design of a mixed mail feeder which can efficiently and reliably process a wide range of different types of mixed mailpieces has been extremely difficult to achieve. The mail handling machine needs a portion which has reduced interdocument forces which allows the mailpiece to bottom edge align with the assistance of gravity.
Furthermore, in achieving the mechanical separation of mail, the mail handling machine produces mechanical noise. The reduction of this noise can be difficult to balance with the mechanical design needs of the machine. Much noise can be produced by the various mechanisms of mail handling machine including the separation mechanisms and gap control mechanisms. The noise can impact the functioning of a mail room environment where the mail handling machine is being operated. Over a period of time, noise can induce hearing loss, and cause annoyance and irritation of workers. Therefore, it is favorable to achieve lower operating sound pressure levels in the mail handling machine by using materials and techniques that cure noise problems.